The present invention relates to a semiconductor diode laser for portable single-frequency laser radiation wherein a plurality of laser-active strips with associated optical resonators are provided in a semiconductor body.
Single-frequency semiconductor diode lasers are known from the prior art whose radiation remains single-frequency in nature, even given high frequency modulation of the operating current. The structure of such a semiconductor diode laser is characterized in that a plurality of laser-active strips are provided in the respective semiconductor body lying parallel and adjacent one another or linearly behind one another in a layer plane, said laser-active strips being more or less excited, and even modulated under given conditions, relative to the threshold of the excitation for the respective laser-active strip or its optical resonator.
Details regarding such a diode laser are stated in IEEE Spectrum, December, 1983, pages 38-45, incorporated herein by reference. Numerous possibilities for realizing such diode lasers are shown therein, particularly in the figure of page 43. More far-reaching details are disclosed in the publications cited below:
U.S. Pat. No. 4,101,845 (Russer); PA0 4th Intern. Conf. on Integrated Optics and Optical Fibre Comm., 27-30, June 1983, Tokyo, pages 24 and 25 and page 30/31; PA0 Appl. Phys. Letters, Vol. 43 (1983), pages 530-532 and pages 421-423; PA0 Electronic Letters, Vol. 19 (1983), No. 22, pages 926-927; PA0 Appl. Phys. Letters, Vol. 41 (1982), pages 112-114; PA0 IEEE Journ. of Quantum Electronics, Vol. QE 18 (1982), pages 1679-1687; and PA0 U.S. Pat. Nos. 4,277,762 and 4,347,612.
All of the above publications are incorporated herein by reference.
In order to achieve single-frequency laser radiation, the diode lasers disclosed in these publications have such a structure that the laser radiation traverses more than one resonator along its propagation direction. Such embodiments are based on a physical principle that was already known in the early 1960's, particularly for gas lasers. As a result of their interaction, these several optical resonators disposed following one another (Fabry-Perot resonators) have the generated laser radiation at only a single frequency, at least from a practical standpoint. Normally a laser generates laser radiation that comprises a multi-mode spectrum and numerous, even though adjacently disposed, frequencies of the radiation. The laser radiation passing through a serial multiple resonator structure having resonators with a mutually divergent resonant frequency spectrum experiences its frequency selection for a coinciding natural or resonant frequency of the participating resonators.
The cited publication "Fourth Intern. Conf. . . . " shows a semiconductor diode laser in FIG. 1 as indicated above which essentially comprises two semiconductor bodies adjacent to one another at a slight distance which are situated on a heat sink. Active strips are fashioned in the two semiconductor bodies for generating the laser radiation, said active strips residing opposite one another at their end faces and sharing an optical axis. Radiation from the one active strip proceeds into the other active strip and vice versa. In the normal case, the semiconductor bodies have mutually different length dimensions L1, L2 in the direction of this optical axis, these likewise being the length dimensions of the optical resonators formed by the active strips. Let it also be pointed out that the respective width dimension of the individual strips also defines the optically effective resonator length.
FIGS. 12 and 13 of U.S. Pat. No. 4,101,845 shows an embodiment having laser-active strips aligned parallel and side-by-side, their spacing from one another being selected such that an optical coupling in accordance with FIG. 14 results.
A modulation of emitted pure-mode laser radiation can be effected by a modulation of the electrical current to be supplied to the one active strip.
The actually effective optical length of the respective optical resonator containing the corresponding active strip can be varied or tuned, under given conditions, by a controllable dimensioning of the supplied current, so that, overall, a shift of the frequency position of the single-frequency laser radiation generated is also possible (see FIG. 2 in "4th Intern. Conf. . . . ").
As may be seen, it is necessary that the laser-active strips be aligned with extraordinary precision relative to one another in the one or more semiconductor bodies.